What size rear brake master cylinder?

[J-max]

I've spent most the afternoon on this & gone round in a circle.

The trike:

late 90s Vmax with English axle (MK1 ford escort). Compomotive 15" rims 225/50 tyres. Has the disc brake conversion. Not sure of the exact piston size but estimate 30mm. Single piston. 9.5" rotors. Pads app 1.25" tall. Pedal leverage ratio 4.75:1

No idea what master cylinder has been fitted. Looks like it's from a car. Can only read the make Brembo. Body diam is 30mm.

There is some weeping where the reservoir tube joins the body but it's not much. No idea how old the fluid is. Brakes feel mushy.

Thought I'd try & find out what ought to be on there before doing anything or spending money.

I went down the 'would the Vmax OEM one be right' rabbit hole. It's 13mm. Using bike calculations/chart I was getting I need 12mm.

I looked here to check only to find 3/4" (19-20mm) or more being talked about so now I'm lost.

All advice gratefully received.

[Marc H]

I would contact Brembo with any numbers you can find on it.They make everything from high performance street car upgrades to full on race applications.Don't discount that it may be a clutch master also.That mounting sure looks like automotive to me.

[Jack Klarich]

3/4 or 7/8 bore master should work fine

[J-max]

I would contact Brembo with any numbers you can find on it.They make everything from high performance street car upgrades to full on race applications.Don't discount that it may be a clutch master also.That mounting sure looks like automotive to me.

I've correction. It's a Bendix I (i). I'm Dyslexic. It has No 653 but I can't find any info.

From appearance only it looks like a clutch M/C for a Fiat Uno (19mm) so bonus points for you.

[J-max]

posted in error.

[J-max]

3/4 or 7/8 bore master should work fine

3/4 - 7/8 seems big to me. I've now seen a chart for bikes & a calc for cars & they're saying anything from 10mm to 1/2".

Could you give more info on how you arrive at 3/4 please?

[Jack Klarich]

3/4 - 7/8 seems big to me. I've now seen a chart for bikes & a calc for cars & they're saying anything from 10mm to 1/2".

Could you give more info on how you arrive at 3/4 please?

3/4 is close to the Bendix 19mm you referenced, many masters are 3/4-7/8

smaller diameter will work but your pedal travel will increase

[J-max]

Update:

Me being me I had to try the 1/2" oem - otherwise it would have bugged me. Didn't even start to operate the rr brakes.

Made some proper bracketry for the Bendix & fitted an external reservoir (oem size was inadequate for the bigger m/c) & this is doing a good job. Not leaking either - so far.